FIG. 1 shows a ducted fan gas turbine engine 10 comprising, in axial flow series: an air intake 12, a propulsive fan 14 having a plurality of fan blades 16, an intermediate pressure compressor 18, a high-pressure compressor 20, a combustor 22, a high-pressure turbine 24, an intermediate pressure turbine 26, a low-pressure turbine 28 and a core exhaust nozzle 30. A nacelle 32 generally surrounds the engine 10 and defines the intake 12, a bypass duct 34 and a bypass exhaust nozzle 36.
Air entering the intake 12 is accelerated by the fan 14 to produce a bypass flow and a core flow. The bypass flow travels down the bypass duct 34 and exits the bypass exhaust nozzle 36 to provide the majority of the propulsive thrust produced by the engine 10. The core flow enters in axial flow series the intermediate pressure compressor 18, high pressure compressor 20 and the combustor 22, where fuel is added to the compressed air and the mixture burnt. The hot combustion products expand through and drive the high, intermediate and low-pressure turbines 24, 26, 28 before being exhausted through the nozzle 30 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines 24, 26, 28 respectively drive the high and intermediate pressure compressors 20, 18 and the fan 14 by interconnecting shafts 38, 40, 42.
Brush seals are well known in the art and are used within a gas turbine engine to provide a seal around a rotating component which extends between two areas which are held at different pressures. FIG. 2 shows a cross-section of a typical brush seal 210 which is placed around a rotating shaft 212 within a bearing housing for example. The left hand side of FIG. 2 represents a high pressure, HP, or upstream area, with the right hand side being a lower pressure, LP, or downstream area. It will be apparent that, for the case of a gas turbine engine, the shaft 212 is not to scale and a corresponding portion of the annular brush is omitted on the opposing underside of the shaft 212 for the sake of clarity.
The brush seal 210 includes an annular housing 214 which holds a plurality of radially extending wire bristles 216 at a fixed end 218. The annular housing 214 comprises an upstream or front plate 214a and a downstream or backing plate 214b which are fixed to a first component 213 such that the bristles 216 extend radially inwards towards a rotating component 212 at their free ends 220. The free ends 220 of the bristles 216 contact the rotating component 212 in use and are of sufficient density that they impede the air flow from the upstream side to the downstream side of the seal 210 so as to provide a seal. It will be appreciated that there will be a certain amount of air which leaks through, the amount of which will be dependent on a number of variables and is therefore application specific.
FIGS. 3a and 3b show an axial end view of a portion of the brush seal 210 from the HP side as defined by section A-A shown in FIG. 2. As can be seen, the bristles 216 are circumferentially inclined with respect to the surface of the rotating shaft 212 such that they contact the shaft 212 at an angle. The bristles 216 are inclined in the direction of rotation of the shaft 212 such that the free ends of the bristles wipe the rotor 212 during use at a sealing surface 221. The sealing surface profile of the free end faces is typically provided by a suitable machining process such as grinding or cutting process.
The brush seal 210 can be made in a number of ways. The seal 210 shown in FIG. 2 is constructed by arranging the bristles 216 between the axially separated front 214a and backing 214b plates at a required density before welding 222 them in place at the fixed ends 218. The collection of bristles can be referred to as a bristle pack.
The present invention provides an improved brush seal.